1. Field of the Invention
The present invention relates to a two-screen display device that displays two images in different directions.
2. Description of the Background Art
Recently, a Liquid Crystal Display (LCD) that can display a different image according to a viewing angle is becoming popular (for example, see “Dual-view liquid crystal and Triple-view liquid crystal,” Sharp Technical Journal, No. 96, November, 2007). Particularly, a two-screen display device that displays two images in different directions is applied to not only a dual-view display device that enables plural viewers to simultaneously view different images, but also a 3D display device that enables stereo display such that two images are viewed by eyes of the same viewer in consideration of a parallax (for example, see Japanese Patent Application Laid-Open No. 2009-250994 and International Patent Publication No. 2004/011987).
As used herein, the “two-screen display device” should include not only the dual-view display device but also the 3D display device. Hereinafter, a color pixel including red (R), green (G), and blue (B) dots is simply referred to as a “pixel”, and a monochrome pixel corresponding to each dot is referred to as a “sub-pixel.”
There is well known a two-screen display method in which a parallax barrier is used. In the parallax-barrier-method two-screen display device, a sub-pixel (first sub-pixel) that displays a first image in a display region of a display panel and a sub-pixel (second sub-pixel) that displays a second image are regularly (for example, alternately) arranged, and a light shielding film, what is called a “parallax barrier,” which includes plural openings is provided on (front-surface side) the display region. The opening of parallax barrier is disposed between the first sub-pixel and the second sub-pixel, and a given distance is provided between the parallax barrier and each sub-pixel.
For example, when the first sub-pixel is located on the lower left of the opening of the parallax barrier while the second sub-pixel is located on the lower right of the parallax barrier, the first sub-pixel is viewed through the opening of the parallax barrier from the right side toward the front of the display panel, and the second sub-pixel is viewed through the opening of the parallax barrier from the left side toward the front of the display panel. Accordingly, the first image displayed by the first sub-pixel is viewed from the right side toward the front of the display panel, and the second image displayed by the second sub-pixel is viewed from the left side toward the front of the display panel.
The dual-view display device has a configuration in which the first image and the second image are not viewed at the same time from the same viewer by increasing a difference between a range (angle) where the first image is viewed and a range where the second image is viewed. On the other hand, the 3D display device has a configuration in which the first image and the second image can simultaneously be viewed with eyes of the same viewer by decreasing the difference between the range where the first image is viewed and the range where the second image is viewed. That is, the dual-view display device and the 3D display device have the same basic structure. The range (angle) where each image is viewed is defined by a size of the opening of the parallax barrier or the distance between the parallax barrier and the pixel.
As can be seen from the above description, in the parallax-barrier-method two-screen display device, a half of the plural sub-pixels disposed in the display region is used to display the first image, and other half is used to display the second image. Accordingly, resolution of the first image and resolution of the second image displayed by the two-screen display device become substantially a half of the resolution possessed by the display device, which results in degradation of image quality.
In the parallax-barrier-method two-screen display device, the first sub-pixel and the second sub-pixel are horizontally arrayed with the opening of the parallax barrier interposed therebetween. Therefore, when the sub-pixels are simply arrayed without changing the size of each sub-pixel or changing a horizontally in-line array of the red (R), green (G), and blue (B) sub-pixels constituting one pixel (color pixel), compared with a usual display device that displays only one screen (hereinafter, referred to as “one-screen display device”), the vertical resolution is identical but the horizontal resolution is a half.
In order that the resolution of the first image and the resolution of the second image are increased while the size of the display region is kept constant, the size of each sub-pixel is reduced to narrow a pitch of the sub-pixel, and the number of pixels arrayed in the display region is increased. For example, when the number of pixels is increased in the liquid crystal display device, it is necessary to increase the number of source lines that supply image signals to the pixels or the number of gate lines that drive the pixels according to increasing number of pixels. Therefore, a production cost increase is generated in order to increase the resolution of the display device.
When the pitch of the sub-pixel is narrowed in the two-screen display device, the range (angle) where the first image and second image are viewed is narrowed. In order that the resolution is increased while the range where the first image and second image are viewed is kept constant, it is necessary to narrow the distance between the parallax barrier and the pixel. For example, in the liquid crystal display device, when the distance between the parallax barrier and the pixel is defined by a thickness of a substrate (color filter substrate) on which a color filter or a black matrix is mounted, it is necessary to thin the substrate, and possibly a production process of the display device of the background art is hardly applied, which results in the production cost increase.